The present invention relates to a rack and pinion power steering apparatus and, in particular, to an integral bushing assembly for a rack and pinion power steering apparatus.
A typical hydraulic rack and pinion power steering apparatus for a vehicle includes a rack that extends axially through a chamber inside a hydraulic cylinder, or housing. The ends of the rack project axially outward from the terminal ends of the housing and are connected with steering linkage that connects to steerable vehicle wheels.
A piston is fixed to the rack within the chamber. Rotation of the vehicle steering wheel actuates a hydraulic valve and causes hydraulic fluid under pressure to act against the piston. The force exerted by the hydraulic fluid moves the piston within the chamber, causing the rack to move axially. The axial movement of the rack moves the steering linkage that, in turn, causes the steerable vehicle wheels to turn.
To prevent hydraulic fluid from flowing out of the chamber, it is necessary to seal the ends of the chamber through which the rack projects. It is also desirable to support the rack for axial movement within the chamber without losing the integrity of the seal. A bushing and seal assembly is typically used for this purpose. It is known to enclose the ends of the chamber with bellows attached to the housing to prevent the ingress of moisture, dirt, or other contaminant into the housing and bearing surfaces.
An apparatus that allows the secure connecting of the bushing to a plain, unmachined end of the housing, and the bellows, with a minimal number of separate pieces would increase service life of the apparatus while decreasing assembly time and production cost.
One feature of the present invention is a fluid power assisted rack and pinion steering apparatus for a vehicle. The apparatus comprises a rack connectable with steerable wheels of the vehicle, a housing partially enclosing the rack and defining a fluid chamber, a bushing encircling the rack, a sleeve supporting the rack for sliding movement relative to the bushing, and a fluid tight seal member for sealing the fluid chamber. The rack has a longitudinal axis and is movable in opposite axial directions to turn the steerable wheels in opposite directions. The bushing has opposite axial ends and is secured in the housing by an interference fit between an outer surface of the bushing and an inner surface of the housing. The sleeve is press fit against a first recessed surface in the bushing of a first diameter. The sleeve thereby extends between the bushing and the rack and engages the rack. The seal member is located adjacent a second recessed surface in one axial end of the bushing. The second recessed surface is of a second diameter greater than the first diameter. The seal member encircles the rack and extends between the rack and the housing. The seal member further sealingly engages both the rack and the housing.
Another feature of the present invention is a fluid power assisted rack and pinion steering apparatus for a vehicle. The apparatus comprises a rack connectable with steerable wheels of the vehicle, a housing partially enclosing the rack and defining a fluid chamber, a bushing encircling the rack, a sleeve supporting the rack for sliding movement relative to the bushing, and a fluid tight seal member for sealing the fluid chamber. The rack has a longitudinal axis and is movable in opposite axial directions to turn the steerable wheels in opposite directions. The housing has at least one terminal end portion with a cylindrical inner surface having a constant inner diameter. The bushing has an outer surface engaging the inner surface of the housing. The sleeve is press fit into a first recess at an inner diameter of the bushing. The seal member encircles the rack and extends between the rack and the housing. The seal member is located in a second recess at an axial end of the bushing.